The karyotypes (2n equals 22) of the Chinese (CH) and Armenian (AH) hamsters are virtually identical in their chromosome banding sequences. Yet, the response of each species to the carcinogenic effects of N-Methyl-N-nitrosourea (MNU) differs strikingly. In addition, the CH responds more readily to ethylated nitroso compound derivatives, such as EMS, ENU, and DEN, in contrast to the AH which is highly responsive to the corresponding methylated derivatives, MMS and MNU. The feasibility of detecting specific mutagenic patterns that might reflect the resistance (CH) or the susceptibility (AH) to MNU carcinogenesis is presented, with attention given to assessing the frequencies and distributions of chromosome breakage (CB) and sister-chromatid exchanges (SCE) in different cultured (target) cell types. The spectrum of cell lines includes derivatives from autoimmune-prone genotypes and preneoplastic lesions. The latter will be derived from explants of pancreatic ductal-cell sarcomatoid proliferations stemming from the self-replicating toxicity induced in both species by adjuvant. Initial studies will concentrate upon BrdU- and MNU-induced CB and SCE, with the different cell types serving as the variables. Thereafter, comparative assessments will be extended to include the mutagenic patterns associated with ethylated vs. methylated derivatives of representative nitroso compounds.